Attach two plates in a ‘plus-sign’ design. Be sure the holes line up where they cross! Then take a bushing and attach it to the plates as shown. Make sure the smooth edge faces up and the notched edge is touching the plate.

Slide an axle through the plates and bushing. It is a good idea to secure the plates with a second bushing. Then slide the other end of the axle through a rotation sensor. Use bushings to secure the sensor also.

Use thick paper, index cards, or cups to create sails. Tape or clip these to the plates. Attach the rotation sensor to the RCX. Make sure to plug the sensor into port 1.

Have students write a program in investigator in ROBOLAB:

Write a program in level 1 to record rotation sensor data for a certain length of time.

Adjust sampling rate to a very small interval (decimal).

Download and run the program to measure the speed of the fan blades as you blow on them or from outside in the wind.

Have students upload and analyze the data:

Upload the data to investigator.

You will want to convert data from sixteenths of a rotation into full rotations. Use the compute tool to divide the data in the red bin by 16.

Look and the chart and note trends. What happens when the wind blows harder? softer? How fast did the wind blow? How slow?

Extensions:

Experiment with different types of arms to see what works best (different material for blades/longer blades/wider blades/narrower blades/angled blades/flat blades).
Once you’ve selected a type, try different sizes.